Effect of casting parameters on cellulose acetate membrane morphology and oxygen/nitrogen separation

Abstract

Membrane for oxygen purification have been reported to be competitive for a small scale oxygen production plant (10 to 25 tonnes/day) at 25 to 40 % oxygen (O2) purity. In order to overcome the trade-off between permeability and selectivity of the membrane, industries are always looking for ways to find a cost effective membrane system. Reducing and minimising the use of chemicals in membrane production will lead in achieving this intention. Therefore in this study, binary dope solution which involved only two chemicals (cellulose acetate (CA) and N-methyl-2-pyrrolidone (NMP)) were used. The aim of this study was to evaluate the effect of casting parameter towards membrane morphology and gas separation performance of CA membrane. For the methodology, CA polymer was dissolved in NMP solvent and fabricated using dry/wet phase inversion technique with three different parameter, first, at the different coagulation bath temperature, second at different solvent evaporation time, and at different coagulation bath composition. The membrane produced was coated with low-viscosity poly(dimethylsiloxane) to cover defects. The prepared membrane morphology was analysed using scanning electron microscope and gas separation performance was tested using soap bubble meter with pure oxygen and nitrogen gasses. Coagulation bath temperature, solvent evaporation time and coagulation bath composition involved in the phase inversion process were significantly influenced the structures and transport properties of the resultant membranes. It was found that, the highest selectivity obtained in this study was 14.95 at optimum conditions of 25 °C, 10 % NMP coagulation bath with 5 seconds solvent evaporation time and 10 % NMP in coagulation bath. This optimised membrane had successfully produced 29.38 % of oxygen purity when tested with compressed air. Hence, it can be said that, this membrane for oxygen purification will be suitable for industrial.